mlabs-haskell / mlabs-haskell/lambda-buffers

Rust codegen Phantom handling bug

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codegen
Dominant language
Haskell
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Description

Phantom handling in Rust codegen is not correct I believe https://github.com/mlabs-haskell/lambda-buffers/blob/401f8a920a557c71440795174da199a1e128c4f9/lambda-buffers-codegen/src/LambdaBuffers/Codegen/Rust/Print/TyDef.hs#L177

record CreateScriptsRequest a = {
  scripts : Map ScriptHash (ScriptDatum a)
  }
derive Eq (CreateScriptsRequest a)
derive Json (CreateScriptsRequest a)

record ScriptDatum a = {
  scriptType : a,
  -- ^ Protocol specific script type stored in this UTxO
  redeemer : AssetClass
  -- ^ Wallet containing `$redeemer` must sign the 'delete-script' transaction as an authorization method
}
derive Eq (ScriptDatum a)
derive PlutusData (ScriptDatum a)
derive Json (ScriptDatum a)

creates a

#[derive(std::fmt::Debug, std::clone::Clone)]
pub struct CreateScriptsRequest<A>{pub scripts: lbf_prelude::prelude::Map<lbf_plutus::plutus::v1::ScriptHash
                                  ,crate::cardano::extra::scriptstorage::validation::ScriptDatum<A>>,
                                  phantom_A: std::marker::PhantomData<A>}

#[derive(std::fmt::Debug, std::clone::Clone)]
pub struct ScriptDatum<A>{pub script_type: A,
                         pub redeemer: lbf_plutus::plutus::v1::AssetClass}

There's 2 problems here.

  1. There's no actual phantom types in the original LB type def
  2. Even if there was, we have a problem when phantom values are not made pub in Rust

Contributor guide

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start at lambda-buffers-codegen/src/LambdaBuffers/Codegen/Rust/Print/TyDef.hs around line 177 and inspect how the shown LambdaBuffers definitions become Rust structs. Compare the generated CreateScriptsRequest and ScriptDatum output, checking both the unnecessary phantom_A field and visibility of phantom values. Done means the generated Rust representation matches the source type definitions and handles genuine phantom types correctly.

Written by the indexing model from the issue text.

Assessment

Tech stack
haskell, rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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